The present invention generally relates to apparatus and systems for determining or monitoring the height or level of a liquid in a vessel, for example and without limitation, a storage tank. More particularly, the invention relates to apparatus and systems which obtain and process, for example, translate, signals into the absolute height or level of liquid over at least a portion of the total height of liquid-containing vessel, such as a liquid storage tank.
The height of liquid in a storage tank has been conventionally determined using a float-type mechanical gage. The float, which moves up and down in response to changes in liquid height, is attached to a gage shaft which rotates in response to the movement of the float. Thus, by calibrating the rotational position of the gage shaft with various heights or levels of liquid, the liquid height or level at any given time can be determined or monitored by observing the rotational position of the gage shaft.
In many situations, liquid heights in a great many tanks, e.g., 50 to 100 or more tanks, need to be determined or monitored at the same time. Therefore, it is desirable to provide a system for obtaining liquid height information with respect to each of a plurality of individual storage tanks so that such information can be transmitted to a central receiving or monitoring station.
Various shaft position monitoring systems have been suggested in the prior art. Examples, without limitation of such systems are disclosed in the following U.S. Pat. Nos. 4,137,451; 4,086,580; 4,037,219; 3,959,628; 3,875,406; 3,842,268; 3,808,431; 3,525,094; and 3,328,591.
Devices that have been highly useful and effective in providing accurate measurement of height of liquids in multiple storage tanks are described in Jannotta, U.S. Pat. No. 4,342,996. Such devices, for example, sold by L&J Engineering, Inc., under the trademark L&J Engineering, MCG 2000F, employ light signal sources and coded, rotatable discs which provide different light patterns which are detected by light signal detectors. The detected patterns of light signals are translatable into the height of a liquid in a liquid storage tank. Thus, such a device is used in conjunction with a storage tank which is equipped with a height (or level) gage including a gage shaft which is rotatable in response to changes in the height (or level) of the liquid in the tank. The device includes an instrument shaft which is capable of being associated with the gage so as to be rotatable in response to rotation of the gage shaft.
There is a need for new systems and apparatus for monitoring or determining the height or level of a liquid in liquid-containing vessels, such as a liquid storage tank.